The invention relates to improvements in methods of and in apparatus for treating mixtures of tobacco particles. More particularly, the invention relates to the treatment of mixtures containing a first fraction consisting of fragmentized tobacco ribs and a second fraction consisting of shredded tobacco ribs and/or tobacco leaf laminae.
Tobacco leaves which are to be converted into the fillers of cigarettes or other rod-shaped smokers' products are subjected to a number of treatments prior to entering the distributor (also called hopper) of a rod making machine, e.g., a cigarette maker. As a rule, the first step involves the destalking of tobacco leaves, i.e., separation of tobacco leaf laminae from tobacco ribs. The thus obtained laminae are largely devoid of ribs and are contacted by one or more flavoring agents (e.g., in the form of sauces) prior to introduction into a comminuting machine known as cutter. The ribs are largely devoid of leaf laminae and are thereupon treated separately from the laminae; such treatment involves shredding and the thus obtained shredded ribs are mixed with shredded tobacco leaf laminae. The resulting mixture of the two types of shreds is ready for introduction into the distributor or hopper of a cigarette maker.
Those parts of comminuted leaves which are obtained as a result of cutting of ribs upon separation of ribs from the leaf laminae often contain fragments having a relatively high specific gravity (weight/air resistance) and hence a relatively pronounced stiffness. Therefore, such portions of tobacco ribs (hereinafter called fragments in contrast to shreds) are likely to interfere with the making of satisfactory cigarettes or other rod-shaped smokers' articles, especially in modern cigarette makers which are designed to turn out up to and in excess of 10,000 articles per minute. Consequently, the fragments of ribs should be, and normally are, separated from satisfactory comminuted ribs (namely acceptable shredded ribs) as well as from shredded leaf laminae. In many instances, the relatively heavy fragments are separated from shreds (of ribs and leaf laminae) in a cigarette making machine proper. The reason is that, in order to make a satisfactory tobacco filler, it is necessary to form a stream of loose tobacco particles (shreds) and, since the fragments are heavier than the shreds, the separating step can be carried out by resorting to relatively simple and convenient pneumatic separation or classification. Such pneumatic separation or classification involves the entrainment of the relatively lightweight shreds by one or more streams of a gaseous carrier fluid which is incapable of entraining the heavier fragments of tobacco ribs.
A drawback of heretofore known procedures of separating fragments of tobacco ribs from the shreds is that the mixture of fragments and shreds also contains a rather high percentage of shredded leaf laminae and/or ribs which, however, are present in such formations that they behave (for example, in a gaseous carrier fluid) not unlike undesirable fragments of tobacco ribs. The formations include coherent shreds, clumps of interlaced shreds and/or crimped or crimpled shreds whose configuration and/or other characteristics are such that they cannot be readily separated from undesirable fragments of tobacco ribs. For example, tobacco which has been treated with relatively high quantities of one or more flavoring agents in the form of sauces or the like will yield satisfactory shreds many of which, however, are bonded to each other by one or more flavoring agents to constitute relatively large accumulations having a relatively high specific weight. Furthermore, the presence of one or more flavoring agents enhances the tendency of otherwise satisfactory shreds to become interlaced and to form clumps which behave not unlike accumulations of coherent (bonded-together) shreds. Still further, the addition of one or more sticky flavoring agents enhances the tendency of individual shreds (or two or another small number of shreds) to undergo a pronounced crimping action and to be thus converted into globules or like configurations which, too, cannot be readily segregated from unsatisfactory or unacceptable fragments of tobacco ribs.
On the other hand, and since tobacco constitutes by far the most expensive constituent of a rod-shaped smokers' product, it is desirable for reasons of economy to salvage as many shredded tobacco particles as possible, i.e., to separate from unacceptable fragments of tobacco ribs all those shreds or groups of shreds (be it shreds of leaf laminae or shreds of ribs) which would be acceptable for use in the making of tobacco fillers save for their tendency to adhere to each other as a result of bonding or interlacing or to assume configurations departing from those of the majority of shreds, e.g., because portions of each such individual shred are bonded to each other by a flavoring agent.